Mass flow rate meters may be used to measure rate of mass flow of particulate materials within a system. Typically the particulate material is dropped onto an impact sensor or thrown against an impact sensor. The force exerted on the impact sensor is relative to the quantity of particulate material moving through the system. The movement or deflection of the impact sensor is converted by a transducer to a calculated mass flow rate.
These mass flow rate meters measure the force of airborne particulate materials which strike an impact sensor. Many materials are not suitable for dropping or throwing at a sensor. These materials would include harvested fruit and vegetable crops and other perishables.
Harvested fruit and vegetables are typically moved on a conveyor belt or chain. These conveyor systems may use scales to determine the mass flow rate of material moving along the conveyor.
Belt scales are a combination of an endless belt or chain of a conveyor with a weighing machine located under a portion of the endless belt The belt scale is disposed to sense the weight of a portion of the material on the belt that is immediately above the weighing machine. It is well known that there is no simple and direct correlation between true mass flow rate passing on the belt. The difference between maximum and minimum flow rate that can be accommodated with out re-calibration of the scale is very limited. A belt scale tends to be sensitive to changes in the humidity of the air as well as to the degree of moisture, or lack thereof, in the material being weighed. It should also be noted that the cost of a belt scale is high.
Belt scales are also undesirable for use on harvesting equipment. Belt scales are often too fragile to be mounted on the moving frame of harvesting equipment. A belt scale also would be inaccurate if the harvesting machine is operating on side slope. A belt scale also would measure soil which is included with the crops which would render the measurement inaccurate.
For the foregoing reasons there is a need for a flow rate measuring device for use with conveyor systems. There is a particular need for a mass flow rate measuring device which is suitable for use on fragile or perishable materials such as fruit or vegetables that are moving along conveyor equipment. There is also a need for a flow rate measuring device which has the necessary durability for use on conveyor systems of harvesting equipment. There is a need for a flow rate measuring device for use on conveyor systems of harvesting equipment which does not produce an inaccurate measurement if soil is included with the crops. There is also a need for a flow rate measuring device for use on conveyor systems of harvesting equipment which is not effected by the pitch or roll of the equipment when operated on a slope. There is also a need for a flow rate measuring device for use on "lifters" or lifting conveyors of harvesting equipment for sugar beets, potatoes, and other crops. These "lifters" or lifting conveyors lift the harvested crop out of the ground and convey the crop to the main conveyor system of the harvester.